An increasingly important consideration when planning the synthesis of biological active organic molecules is the introduction of chirality. One method to achieve this is to use a chiral catalyst, such as an enzyme, which are highly enantiose/ective and specific, a feature that facilitates the preparation of target chirat pharmacologically active compounds. An additional property that makes these biocatalysts attractive to the organic chemist, is that their properties, such as enantioselectivity, prochiral selectivity and specificity are controlled by organic solvents (when used as the reaction medium). Olso, enzymes are inexpensive, they can be "recycled" and are non toxic. Unfortunately there are some drawbacks that limit their applications and potential. The root of the problem is that the mechanism of enzymatic catalysis in non-aqueous media is still not well understood, and consequently a trial and error approach is usually needed to find the best medium, enzymes and conditions. The goal of this study is to elucidate the mechanism by which organic solvents influence enzymatic stereoselectivity, activity and stability, and thereby enable the rational design of stereoselective systems using the physicochemical properties of the substrate and solvents, together with the enzyme structure. We propose to use a combination of experimental and theoretical methods (enzyme kinetics, sophisticated molecular-modeling and NMR methods) to understand the role of the medium in shaping a biocatalyst structure, activity and stereoselectivity.